Pre-lubricants are oil based, metal working fluids generally applied to metal stock in early stages of processing. The pre-lubricant materials form an oily film on the stock which prevents corrosion during storage and handling, and lubricates the metal during subsequent stamping, drawing or other forming operations. Prelubricants are of particular utility in metal working operations involving steel and aluminum stock, but are also used in conjunction with other metals. Ideally, a prelubricant material should be a good corrosion inhibitor and should have good film forming properties so that it can provide a continuous, oily, protective film on the metal stock. Furthermore, pre-lubricants should provide sufficient lubricity to facilitate the metal forming operations. There are presently available a number of prelubricant compositions and they typically comprise an oil base together with corrosion inhibitors, film forming agents and similar ancillary ingredients.
If the formed metal parts are subsequently painted, plated or otherwise finished it is also desirable that the pre-lubricant composition be readily removable so as to prevent interference of the oil base with finishing operations. Because of concerns relating to the cost, toxicity, flammability and the general undesirability of a number of organic solvents, manufacturers are turning increasingly to the use of aqueous based metal finishing processes. Heretofore employed organic based paint formulations are being replaced by aqueous compositions; and organic degreasing baths are being replaced with systems employing aqueous detergents for removing the pre-lubricant.
In a typical finishing process, such as that employed in the manufacture of automobiles, a formed metal part is cleansed of pre-lubricant material in a two-stage process. The first step is a prewash utilizing aqueous detergents, surfactants and the like. This is usually followed by one or more wash steps utilizing similar chemistry. Washing is typically carried out until water drains from the formed metal part in a uniform, break-free sheet, such draining being considered indicative of the lack of oil residue on the part. The washed part is then treated in an aqueous based zinc phosphate containing bath. If oil residue is present on the part, the zinc phosphate coating will be thin, or absent, and later applied paint layers will form craters or other undesirable surface irregularities. Following the zinc phosphate treatment, the formed metal parts are primed, typically in an electrocoat primer bath.
As is well known to those of skill in the metal finishing arts, electrocoat primer paint is typically a water based composition including various proprietary resins, alcohols and the like. The parts are totally immersed in the bath and an electric field is established therethrough to facilitate the deposition of the paint coat on the part. Following the electrocoat step, a finish paint coat, typically comprised of one or more paint layers, is applied.
The pre-lubricant material can cause several problems in such a process. As mentioned hereinabove, oily residue on the surface of the part can result in poor formation of a zinc phosphate coating and can subsequently cause irregularities in the electrocoat layer. Irregularities in these layers are manifested, and often magnified, in the final finish paint coat.
Although it is desirable to remove the entirety of pre-lubricant residues from the part subsequent to final painting, this goal is frequently not achieved. While washing steps can remove residues from a large area, relatively flat portion of the formed article, metal parts frequently include crevices, folds, seams and like configurations which can trap pre-lubricant material preventing it from being removed in the washing steps. While traces of oil on such interior surfaces are not visible to the eye and hence do no significantly interfere with the quality of the final paint finish, their effects are actually far more serious than cosmetic.
Electrocoat baths are of necessity very large so as to accommodate automobile body panels and the like. These baths frequently contain 10,000 gallons or more of electrocoat paint. This paint is quite expensive and filling a single bath represents a very significant cost to a manufacturer. These baths are replenished as needed, but they are seldom drained because of the expense of raw materials and the undesirability of down time. Traces of pre-lubricant composition trapped in crevices and the like may be leached out of formed articles during painting operations and can contaminate the electrocoat baths and/or finish paint baths. The contaminated bath will produce poorly painted parts and the finished items may manifest defects such as craters, fisheyes and various other irregularities in the final paint coat. Obviously, contamination of a large volume paint bath is an extremely costly accident which necessitates repainting of all of the articles produced in the bath as well as scrapping of the expensive bath.
It will be appreciated that there is a great need for a pre-lubricant composition which is readily removed from formed metal parts by aqueous cleaning solutions; even more importantly, there is needed a pre-lubricant composition which is compatible with various paint baths, and hence will not contaminate them if it is inadvertently introduced thereinto. The present invention provides for a pre-lubricant composition which not only protects metal during handling and lubricates it during forming operations, but which is compatible with aqueous paint formulations. By "compatible" in the context of the present invention is meant that contamination by traces of the pre-lubricant composition does not adversely affect the function of the aqueous based paint baths. The pre-lubricant of the present invention, although an oil-based material, disperses and/or solubilizes into the electrocoat or other paint bath thereby preventing spoilage of the bath.
These and other advantages of the present invention will be readily apparent from the discussion, description, examples and claims which follow.